soc: esp32s2: add initial soc support files for esp32s2

by adding specific soc files for esp32s2 bring-up, such as:
- linker script
- soc initialization code
- initial device tree source files
- esp32s2 saola board support.

Signed-off-by: Glauber Maroto Ferreira <glauber.ferreira@espressif.com>

dts/xtensa/espressif/esp32s2.dtsi

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2021 Espressif Systems (Shanghai) Co., Ltd.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <mem.h>
+
+/ {
+	#address-cells = <1>;
+	#size-cells = <1>;
+
+	cpus {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		cpu0: cpu@0 {
+			device_type = "cpu";
+			compatible = "cadence,tensilica-xtensa-lx7";
+			reg = <0>;
+		};
+	};
+
+	soc {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		compatible = "simple-bus";
+		ranges;
+
+		sram0: memory@3ffb0000 {
+			compatible = "mmio-sram";
+			reg = <0x3ffb0000 0x50000>;
+		};
+	};
+
+};